The role of habitat complexity on biodiversity is a fundamental question in ecology. It remains hotly debated in both terrestrial and aquatic environments and a cornerstone of ecology is that increasing habitat complexity promotes species richness and abundance. The topic became popular in aquatic environments as they are faced with intense biological and physical pressures. Most studies have focused on the habitat complexity provided by a single or few foundation species. Maërl beds are ecologically important marine biogenic habitats founded on a few species of free-living coralline algae that aggregate and form highly complex structures. These habitats’ notable diversity levels have been justified by the habitat complexity that they provide. However, most failed to directly test this hypothesis. Using long-term monitoring data, we investigated the effects of habitat complexity on local, regional and temporal diversity patterns of maërl-associated macrofaunal communities. We studied 10 mäerl beds along 300 km of Brittany’s coastline (France) and quantitatively demonstrated that habitat complexity varied in different environmental conditions. We provided evidence that habitat complexity promotes species richness, and that its effects alone are relevant to the diversity patterns among beds and community stability. Our results have important implications for conservation, and we suggest that management should focus on protecting the foundation species themselves. As such our results contribute to the understanding of the fundamental ecological importance of habitat complexity.
Keywords: Habitat complexity, rhodoliths, coralline algae, broad-scale monitoring, beta diversity, community stability.
